1900 S. S. BUCKMAN — EXCURSION NOTES 189 



The point is this : — That of the water which falls on the 

 Marlborough Downs very little finds its way to the 

 Kennet ; it soaks down through pervious Chalk and is 

 drained away by the Salisbury Avon which has the advan- 

 tage of the lower level. And if the river bottom of the 

 Kennet were at all leaky that water would be taken by the 

 Avon. It is a very pronounced case of river robbery. 

 And further, the more a river robs, the more it is en- 

 couraged to rob ; for the robbery itself enables it to eat 

 its way back into its neighbour's territory. 



However, the Salisbury Avon has not got it all its own 

 way. It is, and has been successfully attacked by the 

 Bristol Avon. 



The diagram (Fig. 17), which is at right angles to the 

 last, along the axis of the anticline, shows the relative 

 position. One of the Bristol Avon's streams is draining 

 the ground below the Salisbury Avon, and as it can give 

 a quicker fall in a shorter distance, it will certainly eat 

 into the territory of the Salisbury Avon, and get stronger 

 in the process. Already it has beheaded the stream 

 immediately west of the Sahsbury Avon, one which, rising 

 from the anticline just south of Devizes, cut the pass 

 through the Chalk from West Lavington to Tilshead:"* cut 

 that pass down to 418 feet, or within some 30 feet of 

 what the Sahsbury Avon has done. So the capture must 

 be fairly recent. 



The present position of the Bristol Avon in relation to 

 the Pewsey Yale and the Salisbury Avon may be exactly 

 compared to the state of affairs depicted in Fig. 13 as 

 regards the growing Severn, when part of the Lias vale 

 was drained by streams which flowed through the Chelt 

 gorge of Oolite. What the Bristol Avon is to the Sali.s- 

 bury Avon now, so was the Severn to the then extended 



* Tliis is now the beheaded stream which flows by Winterbouriie — the name means 

 much in river-robbery. Winterbourne indicates shortage of supply in summer. 



